In hospitals or other health-care settings, it is frequently necessary to observe critical physiological conditions of a patient, including cardiovascular conditions. Cardiovascular condition data is obtained from sensors applied to a patient, or by imaging and sensing devices. Further, cardiovascular data may be data reported by a cardiologist based on review of a patient or a patient's monitor or image data. Hospitals or health-care centers often have hundreds or even thousands of sensor and metering devices and hundreds or even thousands of cardiac patients that require monitoring periodically over a lifetime. This data may be stored in a database for archival functions and later retrieval.
A known ECG management system, the MUSE® (Marquette Universal System for Electrocardiography) system of GE Marquette Medical Systems, Inc., is a software-based product that runs on off-the-shelf hardware. In particular, this ECG management system comprises a database of ECGs plus applications software. The MUSE® system receives ECG data from a multiplicity of instruments via a plurality of networks, analyzes that ECG data using various programs such as a serial comparison program, generates reports containing the results of the analysis, and then routes those reports to various systems and peripheral devices. In particular, the MUSE® system has automatic report routing which can send reports to multiple devices, including a facsimile machine as well as a digital pager.
In the known system, each ECG received by the MUSE® system has been analyzed by the instrument which acquired the ECG. Each instrument incorporates ECG analysis programs such as 12SL® from GE Marquette Medical Systems, Inc., which is a computer program for analyzing simultaneously acquired 12-lead ECGs. The 12SL® program makes precise measurements of recorded cardiac signals, and then provides an interpretation of the ECG waveforms using ECG interpretation criteria for both rhythm and morphology. This generates diagnostic statements. The ECG information stored by MUSE® system contains waveforms, measurements and diagnostic statement. The serial comparison program uses all of these. It can also re-measure the waveforms and recalculate measurements and criteria. The serial comparison program can do this on both the current and previous ECG.
A program's accuracy is directly dependent upon the quality of the signal it acquires. In 1979, Marquette introduced an electrocardiograph that simultaneously acquired all of the leads from the 12-lead electrocardiogram. Prior to this time, all commercially available electrocardiographs could only acquire 3 leads at a time. Simultaneous recording was adopted so that the computer could use all signals from all 12 leads to properly detect and classify each QRS complex. The program also applies digital filters which remove power line noise and baseline sway.
Computer measurement of features within the QRS complex is very susceptible to artifact. In addition to filtering, there is another method of eliminating noise from the QRS complex: signal averaging. Instead of analyzing a single QRS complex, the Marquette 12SL® program generates a median complex. That is, it aligns in time, all of the QRS complexes of the same shape; it then generates a representative complex from the median voltages that are found at each successive sample time. This is more complicated than an average, but the method results in a cleaner signal since it disregards outliers.
All ECG computer programs are composed of two parts: one which measures the waveforms, the other which does the interpretation based on these measurements. The main task of the measurement section is to find the location of the major reference points (that is, the onsets and offsets of the P, QRS and T complexes). Consistent with the signal processing portion of the 12SL® program, the onsets and offsets of the major waves are delineated by an analysis of the slopes in all 12 simultaneous leads. That is, QRS duration is measured from the earliest onset in any lead to the latest deflection in any lead. Similarly, the QT interval is measured from the earliest detection of depolarization in any lead to the latest detection of re-polarization in any lead.
After the onsets and offsets of the P, QRS, and T complexes have been demarcated, the waves within each complex are measured according to published standards. These amplitudes and durations result in a measurement matrix containing more than 1600 values. This is then passed to the criteria portion of the 12SL® program so that it can generate an interpretation, including diagnostic statements referenced via a statement library.
The MUSE® system stores ECGs in such a fashion that they can be re-analyzed by the 12SL® program. That is, the fidelity of the stored ECG is such that it can be used as if it were freshly acquired from the patient.
Computerized electrocardiography has resulted in two practical advantages for the overreading physician. First, the computer serves as an additional expert opinion. Second, it is possible for cardiologists to overread computer-analyzed tracings in half the time required for conventional, non-analyzed ECGs. Therefore, the computer is not only used to efficiently record, store, transmit, and present the ECG—it is also used to assist the physician in overreading the ECG.
Marquette's serial comparison program helps reduce the number of unnecessary admissions to coronary care units (CCUs) by speeding the evaluation of “questionable” or “borderline” ECGs. The program, which runs on the MUSE® system, compares a patient's current ECG with previous ECGs. The technique of comparing the current ECG to the previous ECG of a patient is termed serial electrocardiography. Serial electrocardiography is used to identify changes in the patient's electrocardiogram. The Marquette serial comparison program was developed to use statements, ECG measurements and waveform comparison techniques to maximize performance and accuracy in the detection of clinically significant changes in rhythm, P, QRS, ST and T waves. The Marquette MUSE® system, which stores ECGs with physician-edited interpretations to both individual ECGs and serial comparisons, in tandem with the serial comparison program, allows for accurate and expedient processing of a patient's ECG data. It completes the comparison within minutes, and returns the report while the patient is still in the emergency room. Serial comparison saves time and money by promptly providing diagnostically useful information that helps reduce unneeded CCU admissions.
Serial comparison can provide a quick evaluation of many difficult-to-interpret ECG features, including the borderline Q waves of possible myocardial infarction, the mild ST segment elevation of possible myocardial injury and moderate ST segment elevation with Q-wave evidence of myocardial infarction, which may be persistent change resulting from old infarction. The precise, computerized comparison helps the physician to determine whether the patient has experienced an infarction, whether it is old or new, or whether the ECG reflects a variation that is normal for that patient.
Serial comparison is extremely quick and easy to use. The ECG in question is transmitted from the acquiring electrocardiograph to the MUSE® system using an automatic request for serial comparison of the patient's current and past ECGs. (The MUSE® system automatically stores a patient's successive ECGs.) Within minutes, the physician receives a serial comparison report, including previous ECGs, so that the physician can make his/her own visual comparisons.
It is normal to have significant day-to-day variation in the ECG waveform, and an ECG management system must be able to discriminate between normal and clinically significant variations. Certain clinical conditions can only be reliably detected via a serial analysis. The serial comparison program can detect a new left bundle branch block (LBBB) in an ECG series. It does this based on the ECG interpretation as well as direct comparison of the waveforms.
Acute myocardial infarction (a heart attack) is the leading cause of death in the United States of America. Acute myocardial infarction is often detected through serial change. The pertinent clinical changes in the ECG waveform include a small change in the so-called ST segment and a small new Q wave. These changes in the ECG waveform are typical of the evolution of acute myocardial infarction and must be detected in the face of normal variation.
Treatment via thrombolytic therapy (involving dissolution of a thrombus in an artery or the heart) is now indicated if a patient has a new LBBB in the presence of symptoms associated with acute myocardial infarction. The outcome for a patient with this clinical scenario is excellent, even superior to an acute myocardial infarction that only exhibits ST elevation. But time-to-treatment is critical during acute myocardial infarction. This cardiovascular change must be quickly identified and treatment must be immediately applied. There is little benefit in applying treatment when the elapsed time from the onset of chest pain to treatment exceeds 6 hours.
There is a need for a system and a method for providing early detection of a new LBBB in an ECG waveform in the presence of symptoms associated with acute myocardial infarction.